1. Field of the Invention
This disclosure relates to the field of blow mold tooling for use in blow molded plastics, particularly to a blow mold tool including a moveable component which allows for the blow molding of a container with a deeply indented base.
2. Description of the Related Art
Because of the various competing desires in packaging, a large number of products are changing from being packaged in glass or metal to being packaged in plastics. Plastics are generally lighter and more resilient than other packing alternatives, and can be recycled. There are also a wide variety of plastics available which can be selected depending on properties desired to properly hold the products sold in the container. The most common type of plastic containers are probably polyethylene terephthalate (PET) containers which can be blow molded and can provide for a clear finish in the final product which resembles glass.
It is generally well established that it is almost always less expensive to store products packaged in plastic containers in a taller vertical space than over a greater horizontal space. Storing items in a vertically efficient manner means that more items can be stored on a smaller surface area—i.e., less space is needed to store items in a warehouse or retail location. Further, when stacked vertically, items can be transported more efficiently on a smaller surface area resulting in fewer trips. Thus, the ability to easily and stably stack containers is very important and in most storage and transport scenarios, there are always a number of containers of the same size and shape stacked on top of each other.
The stacking of plastic containers, however, is often much more complicated than the placement of one container on top of another container. Most plastic containers provide for an extended neck which is taller than the main body of the container structure. This neck allows for a lid to easily be screwed, snapped, connected or otherwise positioned on and off. At the same time, however, when containers are stacked, generally the higher container in the stack will rest on the lower container's lid or neck due to this vertical extension. When this happens, the weight of that upper container is only distributed across the lid of the lower container (or the rim of the neck if the container is empty). Thus, the weight of the upper container is displaced on a smaller surface area comprised of just the lid (or neck) of the lower container. In this unstable orientation, the shoulder between the neck and the top surface of the container bears significant weight from the stack.
In some cases, the neck is simply unable to bear the necessary weight of the stacked containers above it. For example, in narrow necked containers, the lid or rim is so small when compared to the base of the upper container that the stack is unstable; i.e., the surface area of the base of the higher container is so large that it cannot be supported in a balanced manner by the lid of the lower container, which has a much smaller surface area. Thus, the stacking of these types of containers is generally not possible without supplemental support. One common practice is to place a cardboard or other sheet or support around the necks and between the rims of supporting containers in a stack in order to distribute the force of the containers resting above. Because of the problems inherent to stacking these types of containers, the containers are often distributed in packing boxes which only hold a single layer of containers, but can themselves be stacked, or with sheets of cardboard or another segregating material between the layers of the stack to provide for force distribution.
Even in container designs with wider necks, and thus broader surface areas for stacking, segregating sheets between layers of the stack are often still necessary to prevent the mass of the above containers from being focused too narrowly on the shoulder of the lower container, resulting in overall instability in the stacked container structure and possible malformation of the lower mass-bearing containers in the stack. Thus, even when these wider necked containers have traditionally been stacked for storage or transport, supports are utilized. For example, generally these wider neck containers are positioned to form a first layer. This first layer then has a piece of segregation material placed on it (usually a cardboard sheet), and a second layer is placed on the segregation layer. This process of sandwiching supplemental supports between the layers of containers in the stack is repeated until a desired stack height is obtained. Because of the use of the supplemental supports, stacks in these arrangements could result in containers at the second layer being positioned directly over containers in the first layer, or could result in offsets in the containers between the stacks to further distribute force.
While this form of transport and storage is effective, it has numerous inherent problems. First, this method tends to result in the production of a lot of excess packing material (used as segregation sheets and supports) which are discarded by the end user of the containers. The problem can exist at possibly three different points. The problem exists first when empty containers are stacked and shipped from the packaging manufacturing plant to the plant where they are to be filled. The problem exists again when the containers are filled and shipped to end retailers. The problem can also exist in the transport of used containers to a recycling or refilling facility. Thus, there is a possibility that segregation supports are created and discarded three times for the same load of containers. Second, this method results in excess costs and a loss in efficiency in the moving and storage of containers. The necessary supplemental supports add to the cost of storing and transporting the containers. Further, stacking the containers in this manner with supplemental supports can complicate the stacking and storing process.
U.S. patent application Ser. No. 13/087,883, incorporated herein by reference, describes a container which provides for a recessed portion of the base. This portion allows for a the neck of a lower container in a stack to be placed in the recessed portion of the base of the higher container, resulting in the bottom of the higher container being generally flush with the top of the lower container. This lid-within-base orientation among the stacked containers improves the stackability of the containers and, in eliminating the need for supplemental supports, remedies many of the problems inherent to traditional stacking methodologies (e.g., increased cost, increased waste and decrease efficiency).
However while this lid-within-base design provides numerous benefits for the storage and transportation of containers, currently there are problems in the art in the manufacturing of these recessed base containers.
One problem with the manufacture of these recessed base containers is that it is generally hard, if not impossible, to form the legs of the container around the recessed base. In a traditional blow-molding technique, the two- or three-part mold is closed and the parison or preform is blown into the final container form in the mold. Generally, in currently utilized blow-molding techniques, the neck of the container is associated with the portion of the mold that blows the air into the mold. Further, the base of the container is associated with the portion of the mold opposite from the point where the air is blown into the mold. Because of the trajectory of the air pressure into the preform, which creates the resultant container, it is generally difficult to attain the sharp corners needed to create the legs of the container around the recessed base; the air pressure inserted into the preform simply cannot make the sharp corners in the legs such that the blown-out preform completely fills the legs of mold. The top left and right ninety degree corners of the indent which comprise the recessed base block the air pressure applied at the neck of the container from causing the preform to stretch to this portion of the mold. Accordingly, it can be difficult, if not impossible, with the currently utilized blow-molding technologies to create the fully formed recessed base and legs shown in FIG. 3.
Further, the recessed base of these containers does not lend itself to traditional blow molding techniques with either a two or three part mold. Generally, when the mold is in the forming position (i.e., when the multi-part mold is closed and the parison or preform is being blown into final container form in the mold) there is a sufficient amount of support to retain the integrity of the container.
In this forming orientation, there is usually a raised step portion in the mold which forms the corresponding recessed base in the container. Notably, when the mold is separated into its component parts to release the container, there is an enormous amount of pressure and mechanical stress on the newly formed container. This is especially true for the area of the container surrounding the raised portion of the mold at the base. For example, although it is partially cooled in some processes after being blown into the form, the newly formed blow-molded container generally has not been fully set and stabilized (e.g., it has generally not been completely cooled into a set position and is generally still malleable). Stated differently, although partially cooled, the newly formed container is still vulnerable to malformation.
It is generally impossible to create a recessed blow molded container with a two-part mold. As demonstrated in prior art FIG. 1, the split in two-part molds which opens to the blow mold cavity where the hot parison or preform is placed is generally vertical in orientation. Thus, as seen in FIG. 1, the mold opening and closing action which is necessary to close the mold for container formation and release the formed container after blow-molding is a horizontal action that presses the internal portion of the vertically oriented molds together and apart. In molds which have a raised portion of the blow mold cavity (to create a recessed base in the formed container) the horizontal mold opening action necessary to release the formed container from the mold cavity would tear the base and the container apart.
The formation of recessed blow mold containers is also difficult with traditionally utilized three-part molds. Generally, traditionally utilized three-part molds are comprised of the same component parts of a two-part mold, with the addition of a third part of the mold which is located at the base of the two vertically oriented parts of the mold. Similar to the two-part mold, the cavities of the vertically oriented parts of the mold form the top, neck and side-body portions of the resultant container. The third component part of the mold, the base, forms the base of the resultant container. In order to create a recessed base in the resultant container, the base cavity of the mold generally contains a raised portion or step. In order to release the newly formed container, the base portion of the cavity usually falls vertically from the container. Then, the vertically oriented portions of the container are separated via a horizontal opening action. Alternatively, the vertically oriented portions of the container can be separated first via a horizontal opening action followed by the dropping of the base. One embodiment of a three-part mold of the prior art is depicted in prior art FIG. 2.
Due to the high pressure and mechanical stress exerted on the mold bottom when the container is released, even though there is no a direct conflict between the mold and recessed bottom portion of the container as is present in a two-part mold, the recessed base of the resultant container is subject to stripping and disorientation from the raised step and the rest of the bottom mold cavity retracting simultaneously. Due to the sensitive condition of the recently formed container, and its fragility to malformation and disorientation at this stage, the retraction of the raised step and bottom portion of the mold at the same time places extreme tensile pressure on the newly formed base of the container, increasing the likelihood that the recessed base could become stuck in the blow molding machine or could be unduly and improperly altered. The deeper this recess is, the greater the mechanical forces applied and therefore the increased likelihood of deformation. Thus, even with the traditional three-part mold, there is a high likelihood of malformation of the resultant bold molded container when a container with a recessed base is attempted, if the three-part mold even has the ability to create a mold with a sufficiently deep foot “channel” around the central indent.